The present invention relates to implantable devices, more particularly, programmable implantable pumps allowing for variable flow rates in delivering medication or other fluid to a selected site in the body of a patient.
Implantable pumps have been well known and widely utilized for many years. Typically, pumps of this type are implanted into patients who require the delivery of active substances or medication fluids to specific areas of their body. For example, patients that are experiencing severe pain may require pain killers daily or multiple times per day. Absent the use of an implantable pump or the like, a patient of this type would be subject to one or more painful injections of such medication fluids. In the case of pain associated with more remote areas of the body, such as the spine, these injections may be extremely difficult to administer and particularly painful for the patient. In certain instances, proper application of such medication may be impossible. Furthermore, attempting to treat conditions such as this through oral or intravascular administration of medication often requires higher doses of medication and may cause severe side effects. Therefore, it is widely recognized that utilizing an implantable pump may be beneficial to both a patient and a treating physician.
Many implantable pump designs have been proposed. For example, commonly invented U.S. Pat. No. 4,969,873 (“the '873 Patent”), the disclosure of which is hereby incorporated by reference herein, teaches one such design. The '873 Patent is an example of a constant flow pump, which typically includes a housing having two chambers, a first chamber for holding a specific medication fluid to be administered and a second chamber for holding a propellant. A flexible membrane preferably separates the two chambers such that expansion of the propellant in the second chamber pushes the medication fluid out of the first chamber. It is to be understood that the propellant typically expands under normal body temperature. This type of pump also typically includes an outlet opening connected to a catheter for directing the medication fluid to the desired area of the body, a replenishment opening for allowing for refill of the medication fluid into the first chamber and a bolus opening for allowing the direct introduction of a substance through the catheter without introduction into the first chamber. Both the replenishment opening and the bolus opening are typically covered by a septum that allows a needle or similar device to be passed through it, but which properly seals the opening upon removal of the device. As pumps of this type provide a constant flow of medication fluid to the specific area of the body, they must be refilled periodically with the proper concentration of medication fluids suited for extended release.
Although clearly beneficial to patients and doctors that utilize them, constant flow pumps generally have one major problem, i.e., that only a single flow rate can be achieved from the pump. Thus, implantable pumps have also been developed, which allow for variable flow rates of medication therefrom. These pumps are typically referred to as programmable pumps, and have exhibited many different types of designs. For instance, in a solenoid pump, the flow rate of medication fluid can be controlled by changing the stroke rate of the pump. In a peristaltic pump, the flow rate can be controlled by changing the roller velocity of the pump. Likewise, pumps of the constant flow type have been modified to allow for a variable and programmable flow rate. For instance, commonly owned U.S. Pat. No. 7,637,892 (“the '892 Patent”) teaches such a design. The '892 Patent, as well as related U.S. patent application Ser. Nos. 11/125,586; 11/126,101; and 11/157,437 are each incorporated herein by reference. In each case, the benefit of providing variable flow is at the forefront, so that differing levels of medication can be delivered to the patient at different times.
In the '892 Patent, a constant flow-type pump assembly is modified to include a module that converts the constant flow pump into a programmable pump. That control module includes, inter alia, two pressure sensors, a constant flow capillary, and a valve assembly. The pressure centers are utilized to measure pressure directly from a medication chamber, and pressure just prior to entering the valve assembly. These pressure readings are utilized by a computing unit, which in turn causes a motor to operate the valve assembly to allow lesser or greater flow from the pump. The capillary preferably ensures that a maximum flow rate can only be achieved from the pump. The pump taught in the '892 Patent is indeed a useful programmable pump, but one which may be improved.
One area in which the pump taught in the '892 Patent, as well as pumps taught in other prior art references, can be improved is in allowing for finer adjustment of flow rate from the pump, which is often difficult or impossible. For instance, a pump of the type taught in the '892 Patent may exhibit a nonlinear relationship between movement of the valve and actual flow rate from the pump, which can lead to small changes in valve position resulting in major changes in flow. Of course, a more preferable valve distance and flow relationship would be of the linear type, where the distance is gradually related to the flow rate. Another area in which prior art programmable pumps can be improved is in the sealing of certain components from the body environment in which the pump is implanted. This may be particularly important in ensuring constant operation of the pump, as well as in ensuring the safety of the patient.
Therefore, there exists a need for an improved programmable implantable pump design.